buying graphics card, first time doing anything like this

this is the graphics card i am looking at

EVGA GeForce 8400 GS 512 MB DDR3 PCI Express 2.0 DVI/HDMI/VGA Graphics Card, 512-P3-1300-LR

my comp has 1.99gb of ram XP professional, current graphics card is Intel(R) 82915G/GV/910GL if that's even a graphics card it came with my shitty desktop and apparently it hasn't been updated since 2005, with the most recent update being 2007

i have steam and want to play older games (pre 2007ish) and am not looking to run skyrim or anything crazy like that, and the card i have currently barely runs games that are above 2003 (constant freezing, choppy, laggy) and apparently this card can run games like sims 3 and oblivion which is more then i want

tl;dr, i have no idea what i'm doing basically what i assume will happen is that ill open my computer, put it in, install the drivers and it will work? (apparently these dudes have good tech support so i'm not too concerned)

will this work out well? is there anything i'm fucking up? any more information i can give you that would aid you?

me

considering buying amd radeon hd 6850, if this can have me playing modern games on steam